1. Field of the Invention
The present invention, in general, relates to devices for anchoring of a structure such as the wall or roof of a mine shaft or other opening and, more particularly, to such types of devices that rely upon frictional engagement between the device and the structure to accomplish the anchoring.
Friction rock stabilizers are also referred to in the mining industry as "bolts". They are in general known types of devices. As they are usually inserted into a bored hole by impact or by other force, such as by a hydraulic cylinder urging them into position, they generally require access to the head of the bolt in order to effectively drive them into the structure they are to reinforce (anchor).
Due to the nature of the structure to be anchored a longer type of a bolt is often required. However, the available clearances in mine shafts may preclude the use of a longer bolt where access to the head of the bolt is required. A greater quantity of smaller bolts, may in some instances be used, but this adds both to the time and expense to drill the bore holes and to then install the bolts.
In other instances a longer bolt is necessary to reach certain kinds of strata that are able to bear the weight and the load that is exerted by weaker strata disposed closer to the mine shaft. If the available room precludes such use, individual safety is compromised in these kinds of mine shafts or great difficulty and expense is incurred in an attempt to drive longer types of bolts in areas where clearances are tight.
What is considered a long or a short friction rock stabilizing bolt depends upon the particular circumstances. In certain instances a bolt of only a few feet in length is considered long where in another instance it would be regarded as being short. Similarly, a bolt of 8 feet in length or longer is commonly referred to as a long bolt but in another more unique situation it would be a short bolt.
Of course the disclosure as shown is adaptable for use with friction stabilizing bolts of any length and while situations may arise or be discovered where a bolt of only a few inches in length is useful to secure a structure, normally for most applications these bolts will range in length from a couple of feet long to slightly over 10 feet long.
Accordingly there exists today a need for a Friction Rock Stabilizer type of bolt that provides good anchoring characteristics that is also adapted for use in areas of low installation clearance.
Also these improved friction rock stabilizer bolts, as disclosed herein, have been found on occasion to provide greater retention strength for any given level of insertion force as compared to a conventional bolt of similar length and therefore they are also useful when a lower insertion force is preferred that nevertheless yields an acceptably high retention force.
2. Description of Prior Art
Friction Rock Stabilizer bolts are, in general, known. For example, the following patents describe various types of these devices:
U.S. Pat. No. RE 28, 227 to Elders, Nov. 5, 1974; PA1 U.S. Pat. No. 3,349,567 to Munn, Oct. 31, 1967; PA1 U.S. Pat. No. 3,922,867 to Scott, Dec. 2, 1975; PA1 U.S. Pat. No. 4,012,913 to Scott, Mar. 22, 1977; PA1 U.S. Pat. No. 4,126,004 to Lindeboom, Nov. 11, 1978; PA1 U.S. Pat. No. 4,313,695 to McCartney, Feb. 2, 1982; PA1 U.S. Pat. No. 4,334,804 to Lindeboom, Jun. 15, 1982; PA1 U.S. Pat. No. 4,445,808 to Arya, May 1, 1984; PA1 U.S. Pat. No. 4,607,984 to Cassidy, Aug. 26, 1986; PA1 U.S. Pat. No. 4,798,501 to Spies, Jan. 17, 1989; and PA1 U.S. Pat. No. 4,971,493 to Herbst, et al, Nov. 20, 1990.
While the structural arrangements of the above described devices, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.